The present disclosure relates to cementitious board manufacturing processes and, more particularly, to systems and methods for measuring the hardness of the edge of a cementitious board after its manufacture.
In many types of cementitious articles, set gypsum (calcium sulfate dihydrate) is often a major constituent. For example, set gypsum is a major component of end products created by use of traditional plasters (e.g., plaster-surfaced internal building walls), and also in faced gypsum board employed in typical drywall construction of interior walls and ceilings of buildings. In addition, set gypsum is the major component of gypsum/cellulose fiber composite boards and products, as described in U.S. Pat. No. 5,320,677, for example. Typically, such gypsum-containing cementitious products are made by preparing a mixture of calcined gypsum (calcium sulfate alpha or beta hemihydrate and/or calcium sulfate anhydrite), water, and other components, as appropriate to form cementitious slurry. The cementitious slurry and desired additives are often blended in a continuous mixer, as described in U.S. Pat. No. 3,359,146, for example.
In a typical cementitious board manufacturing process such as gypsum wallboard, cementitious board is produced by uniformly dispersing calcined gypsum (commonly referred to as “stucco”) in water to form aqueous calcined gypsum slurry. The aqueous calcined gypsum slurry is typically produced in a continuous manner by inserting stucco and water and other additives into a mixer which contains means for agitating the contents to form a uniform gypsum slurry. The slurry is continuously directed toward and through a discharge outlet of the mixer and into a discharge conduit connected to the discharge outlet of the mixer. Aqueous foam can be combined with the aqueous calcined gypsum slurry in the mixer and/or in the discharge conduit. A stream of foamed slurry passes through the discharge conduit from which it is continuously deposited onto a moving web of cover sheet material (i.e., the face sheet) supported by a forming table. The foamed slurry is allowed to spread over the advancing face sheet. A second web of cover sheet material (i.e., the back sheet) is applied to cover the foamed slurry and form a sandwich structure of a continuous wallboard preform. The wallboard preform is subjected to forming, such as at a conventional forming station, to obtain a desired thickness.
The calcined gypsum reacts with the water in the wallboard preform to form a matrix of crystalline hydrated gypsum or calcium sulfate dihydrate and sets as a conveyor moves the wallboard preform down the manufacturing line. The hydration of the calcined gypsum provides for the formation of an interlocking matrix of set gypsum, thereby imparting strength to the gypsum structure in the gypsum-containing product. The product slurry becomes firm as the crystal matrix forms and holds the desired shape.
After the wallboard preform is cut into segments downstream of the forming station at a point along the line where the preform has set sufficiently, the segments are flipped over, dried (e.g., in a kiln) to drive off excess water, and processed to provide the final wallboard product of desired dimensions. The aqueous foam produces air voids in the set gypsum, thereby reducing the density of the finished product relative to a product made using a similar slurry but without foam. Dried boards are typically sold in pairs in which the two boards are arranged with their face sheets arranged inwardly (a process called “booking”) to help protect the face sheets from becoming marred during transportation and handling. Booked pairs of boards can be stacked on top of each other at a stacking unit to facilitate bundling and palletization. Prior devices and methods for addressing some of the operational problems associated with the production of gypsum wallboard are disclosed in commonly-assigned U.S. Pat. Nos. 5,683,635; 5,643,510; 6,494,609; 6,874,930; 7,007,914; and 7,296,919, which are incorporated by reference.
Gypsum wallboard is typically installed by securing the board to a framing structure using a plurality of fasteners. The installer follows a fastener schedule in which a number of fasteners are used along the long edges of the board. Typically, more fasteners are required along the edges of the board than are used in the field of the board. Furthermore, during transport of gypsum wallboard, the edges of the board are typically grasped by the installer to manipulate the board.
With the core of the board being made from increasingly less dense gypsum slurry, it can be desirable to position a more dense and/or stronger slurry at the edges of the board to help allow for the handling of the board without excessive damage to its edges and also to allow for the secure attachment of the board to a framing structure via fasteners located at the edges of the board. U.S. Pat. Nos. 2,985,219 and 4,279,673 describe various methods for producing foamed gypsum board having edges that are denser and harder than the core portion of the board, such as, by diverting a portion of the foamed slurry from the main slurry mixing chamber. The diverted portion is then treated separately in one or more supplementary mixers with high agitation and/or defoaming agents to remove all or most of the foam and thus produce a harder, denser “edge” slurry to be cast at the edges of the cover sheet so that it comes into contact with the sides of the cast main slurry stream.
Should the board edges be too hard, other problems can occur. For example, edges that are too hard can produce fastener failures manifested as fasteners being pulled out of the framing structure. Also, when board with edges that are too hard is dropped, it can break at a lateral position along its width that is too far inward and/or to a greater degree, than one would find acceptable.
Gypsum wallboard manufacturers typically evaluate the hardness of the edges of the board to determine the board's ability to resist being crushed during handling or installation. For example, ASTM International's ASTM Standard C473-16, which is entitled, “Standard Test Methods for Physical Testing of Gypsum Panel Products,” sets forth a test procedure for measuring board edge hardness using a steel punch. During the manufacture of the gypsum boards, an operator may periodically test the edge hardness of the dried board to verify that a certain degree of edge hardness is being obtained. For example, an operator can use a handheld hardness tester to assess the hardness of the board edges as the boards come to rest near a stacking machine.
There is a continued need in the art to provide additional solutions to enhance the production of cementitious boards. For example, there is a continued need for techniques for measuring the edge hardness of cementitious boards that have enhanced efficiency and repeatability.
It will be appreciated that this background description has been created by the inventor to aid the reader and is not to be taken as an indication that any of the indicated problems were themselves appreciated in the art. While the described principles can, in some aspects and embodiments, alleviate the problems inherent in other systems, it will be appreciated that the scope of the protected innovation is defined by the attached claims and not by the ability of any disclosed feature to solve any specific problem noted herein.